Hello!
This is a dual band antenna. The "Moxon" part of the antenna works on VHF, while the "Yagi" part of the antenna works on UHF.
The element inside the Moxon rectangle is the reflector of the Yagi antenna, since the rectangle cannot function as a reflector in UHF. The lengths of and spacing between the directors of the Yagi correspond to UHF frequencies.
Best regards
Tony